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        <h1 class="title">Java web:Servlet listener</h1>
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            <ol class="post-toc"><li class="post-toc-item post-toc-level-2"><a class="post-toc-link" href="#学习笔记-Java-web之Servlet事件监听器"><span class="post-toc-number">1.</span> <span class="post-toc-text">学习笔记 : Java web之Servlet事件监听器</span></a><ol class="post-toc-child"><li class="post-toc-item post-toc-level-3"><a class="post-toc-link" href="#概述"><span class="post-toc-number">1.1.</span> <span class="post-toc-text">概述</span></a></li><li class="post-toc-item post-toc-level-3"><a class="post-toc-link" href="#监听域对象的生命周期"><span class="post-toc-number">1.2.</span> <span class="post-toc-text">监听域对象的生命周期</span></a><ol class="post-toc-child"><li class="post-toc-item post-toc-level-4"><a class="post-toc-link" href="#案例-监听域对象的生命周期"><span class="post-toc-number">1.2.1.</span> <span class="post-toc-text">案例-监听域对象的生命周期</span></a></li><li class="post-toc-item post-toc-level-4"><a class="post-toc-link" href="#案例-统计当前在线人数"><span class="post-toc-number">1.2.2.</span> <span class="post-toc-text">案例-统计当前在线人数</span></a></li></ol></li><li class="post-toc-item post-toc-level-3"><a class="post-toc-link" href="#监听域对象中的属性变更"><span class="post-toc-number">1.3.</span> <span class="post-toc-text">监听域对象中的属性变更</span></a><ol class="post-toc-child"><li class="post-toc-item post-toc-level-4"><a class="post-toc-link" href="#案例-监听域对象的属性变更"><span class="post-toc-number">1.3.1.</span> <span class="post-toc-text">案例-监听域对象的属性变更</span></a></li><li class="post-toc-item post-toc-level-4"><a class="post-toc-link" href="#案例-统计当前在线人数名单"><span class="post-toc-number">1.3.2.</span> <span class="post-toc-text">案例-统计当前在线人数名单</span></a></li></ol></li><li class="post-toc-item post-toc-level-3"><a class="post-toc-link" href="#感知被HttpSession绑定的事件监听器"><span class="post-toc-number">1.4.</span> <span class="post-toc-text">感知被HttpSession绑定的事件监听器</span></a></li></ol></li></ol>
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        <h1 class="post-card-title">Java web:Servlet listener</h1>
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            <time class="post-time" title="2019-05-02 09:31:43" datetime="2019-05-02T09:31:43.000Z"  itemprop="datePublished">2019-05-02</time>

            


            

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            <h2 id="学习笔记-Java-web之Servlet事件监听器"><a href="#学习笔记-Java-web之Servlet事件监听器" class="headerlink" title="学习笔记 : Java web之Servlet事件监听器"></a>学习笔记 : Java web之Servlet事件监听器</h2><h3 id="概述"><a href="#概述" class="headerlink" title="概述"></a>概述</h3><p><em><code>Servlet</code>事件监听器可以监听<code>ServletContext</code>,<code>HttpSession</code>,<code>ServletRequest</code>等域对象的创建和销毁过程,监听这些域对象属性的修改以及感知绑定到HttpSession域中某个对象的状态.根据监听事件的不同可以将其分为三类,具体如下 :</em></p>
<ol>
<li><em>用于监听域对象创建和销毁的事件监听器 : ServletContextListener,HttpSessionListener,ServletRequestListener interface</em></li>
<li><em>用于监听域对象属性增加和删除的事件监听器 : ServletContextAttributeListener,HttpSessionAttributeListener,ServletRequestAttributeListener interface</em></li>
<li><em>用于监听绑定到HttpSession域中某个对象状态的事件监听器 : HttpSessionBindingListener,HttpSessionActivationListener interface</em></li>
</ol>
<h3 id="监听域对象的生命周期"><a href="#监听域对象的生命周期" class="headerlink" title="监听域对象的生命周期"></a>监听域对象的生命周期</h3><p><em>简介 : 在Web应用程序的运行期间,Web容器会创建和销毁三个比较的重要的对象: <code>ServletContext</code>,<code>HttpSession</code>,<code>ServletRequest</code>,这些对象被称为域对象,为了监听这些域对象的生命周期,Servlet API中提供了三个对应的接口: ServletContextListener,HttpSessionListener,ServletRequestListener.</em></p>
<h4 id="案例-监听域对象的生命周期"><a href="#案例-监听域对象的生命周期" class="headerlink" title="案例-监听域对象的生命周期"></a>案例-监听域对象的生命周期</h4><p><em>示例代码如下所示</em><br><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@ClassName</span>: MyServletListener</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@Description</span>: 监听域对象的生命周期</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@author</span>: HuangYuhui</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@date</span>: May 3, 2019 3:17:56 PM</span></span><br><span class="line"><span class="comment"> * </span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="meta">@WebListener</span>(value=<span class="string">"/MyServletListener"</span>)<span class="comment">//Servlet 3.0</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">MyServletListener</span> <span class="keyword">implements</span> <span class="title">ServletContextListener</span>, <span class="title">ServletRequestListener</span>, <span class="title">HttpSessionListener</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">contextInitialized</span><span class="params">(ServletContextEvent sce)</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"ServletContext object be initialized !"</span>);</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">contextDestroyed</span><span class="params">(ServletContextEvent sce)</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"ServletContext object be destroyed !"</span>);</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">requestInitialized</span><span class="params">(ServletRequestEvent sre)</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"ServletRequest object be initialized !"</span>);</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">requestDestroyed</span><span class="params">(ServletRequestEvent sre)</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"ServletRequest object be destroyed !"</span>);</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">sessionCreated</span><span class="params">(HttpSessionEvent se)</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"HttpSession object be initialized !"</span>);</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">sessionDestroyed</span><span class="params">(HttpSessionEvent se)</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"HttpSession object be destroyed !"</span>);</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p><em>为了查看HttpSessionListener和ServletRequestListener监听器的运行效果,可以新建一个index.jsp页面,当运行Tomcat服务器第一次访问index.jsp时,Web容器除了为这次请求创建了<code>ServletRequest</code>对象外,还创建了与这个浏览器对应的<code>HttpSession</code>对象,当这两个对象在被创建时,Web容器会调用监听器MyServeltListener中相应的方法,当Web服务器完成这次请求后,<code>ServletRequest对象会随之销毁.</code>需要注意的是: 如果刷新index.jsp页面,会再次触发<code>ServletRequestListener</code>监听器接口中的方法,继而创建新的ServletRequest对象,但不会创建新的HttpSession对象,这是因为<code>Web容器会为每次访问请求创建一个新的ServletRequest对象,而对于同一个浏览器在会话期间的后续访问是不会再创建新的HttpSession对象的.</code></em></p>
<h4 id="案例-统计当前在线人数"><a href="#案例-统计当前在线人数" class="headerlink" title="案例-统计当前在线人数"></a>案例-统计当前在线人数</h4><p><em>案例描述 : 通常情况下,当一个用户在进入某个网站时服务器就会为其创建一个HttpSessionListener对象,当用户离开网站时HttpSessionListener对象就会别销毁.因此,可以使用实现了<code>HttpSessionListener</code>接口的监听器来统计网站的在线人数.</em></p>
<ol>
<li><p><em>login.jsp : 用于显示当前在线人数.</em></p>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">%@</span> <span class="attr">page</span> <span class="attr">language</span>=<span class="string">"java"</span> <span class="attr">contentType</span>=<span class="string">"text/html; charset=UTF-8"</span></span></span><br><span class="line"><span class="tag">    <span class="attr">pageEncoding</span>=<span class="string">"UTF-8"</span>%&gt;</span></span><br><span class="line"><span class="meta">&lt;!DOCTYPE <span class="meta-keyword">html</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;<span class="name">head</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">meta</span> <span class="attr">charset</span>=<span class="string">"UTF-8"</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">title</span>&gt;</span>HttpSessionListener案例: 统计当前在线人数<span class="tag">&lt;/<span class="name">title</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;/<span class="name">head</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">h3</span> <span class="attr">align</span>=<span class="string">"center"</span>&gt;</span>当前在线人数为: <span class="tag">&lt;<span class="name">%=application.getAttribute("count")%</span>&gt;</span><span class="tag">&lt;/<span class="name">h3</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">a</span> <span class="attr">href</span>=<span class="string">"&lt;%=response.encodeURL("</span><span class="attr">logout.jsp</span>")%&gt;</span>"&gt;退出登录<span class="tag">&lt;/<span class="name">a</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br></pre></td></tr></table></figure>
</li>
<li><p><em>CountListener.java : 用于统计当前在线人数.</em></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@ClassName</span>: CountListener</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@Description</span>: 统计在线人数</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@author</span>: HuangYuhui</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@date</span>: May 3, 2019 3:40:59 PM</span></span><br><span class="line"><span class="comment"> * </span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="meta">@WebListener</span>(value = <span class="string">"/CountListener"</span>)</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">CountListener</span> <span class="keyword">implements</span> <span class="title">HttpSessionListener</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">	<span class="keyword">private</span> <span class="keyword">int</span> count = <span class="number">0</span>;<span class="comment">// 在线人数</span></span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="comment">// Session对象创建时count++</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">sessionCreated</span><span class="params">(HttpSessionEvent se)</span> </span>&#123;</span><br><span class="line">		count++;</span><br><span class="line">		ServletContext servletContext = se.getSession().getServletContext();</span><br><span class="line">		servletContext.setAttribute(<span class="string">"count"</span>, Integer.valueOf(count));</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="comment">// Session对象销毁时count--</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">sessionDestroyed</span><span class="params">(HttpSessionEvent se)</span> </span>&#123;</span><br><span class="line">		count--;</span><br><span class="line">		ServletContext servletContext = se.getSession().getServletContext();</span><br><span class="line">		servletContext.setAttribute(<span class="string">"count"</span>, Integer.valueOf(count));</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
</li>
<li><p><em>logout.jsp : 用于注销用户登录.</em></p>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">%@</span> <span class="attr">page</span> <span class="attr">language</span>=<span class="string">"java"</span> <span class="attr">contentType</span>=<span class="string">"text/html; charset=UTF-8"</span></span></span><br><span class="line"><span class="tag">    <span class="attr">pageEncoding</span>=<span class="string">"UTF-8"</span>%&gt;</span></span><br><span class="line"><span class="meta">&lt;!DOCTYPE <span class="meta-keyword">html</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;<span class="name">head</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">meta</span> <span class="attr">charset</span>=<span class="string">"UTF-8"</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">title</span>&gt;</span>HttpSessionListener案例: 统计当前在线人数<span class="tag">&lt;/<span class="name">title</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;/<span class="name">head</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">%</span></span></span><br><span class="line"><span class="tag">			<span class="attr">session.invalidate</span>();// 使当前的<span class="attr">Session</span>失效</span></span><br><span class="line"><span class="tag">		%&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">h3</span> <span class="attr">align</span>=<span class="string">"center"</span>&gt;</span>你已退出本系统<span class="tag">&lt;/<span class="name">h3</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br></pre></td></tr></table></figure>
</li>
</ol>
<h3 id="监听域对象中的属性变更"><a href="#监听域对象中的属性变更" class="headerlink" title="监听域对象中的属性变更"></a>监听域对象中的属性变更</h3><p><em>简介 : Servlet API 中提供了三个用于监听某个域对象属性变更的接口: <code>ServletContextAttributelistener</code>,<code>HttpSessionAttributerListener</code>和<code>ServletRequestAttributeListener</code>.这三个接口都定义了相同名称的方法,分别用于处理被监听对象属性的增加,删除和替换.</em></p>
<h4 id="案例-监听域对象的属性变更"><a href="#案例-监听域对象的属性变更" class="headerlink" title="案例-监听域对象的属性变更"></a>案例-监听域对象的属性变更</h4><ol>
<li><em>attribute.jsp : 设置各个域对象的属性.</em><figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">%@</span> <span class="attr">page</span> <span class="attr">language</span>=<span class="string">"java"</span> <span class="attr">contentType</span>=<span class="string">"text/html; charset=UTF-8"</span></span></span><br><span class="line"><span class="tag">    <span class="attr">pageEncoding</span>=<span class="string">"UTF-8"</span>%&gt;</span></span><br><span class="line"><span class="meta">&lt;!DOCTYPE <span class="meta-keyword">html</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;<span class="name">head</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">meta</span> <span class="attr">charset</span>=<span class="string">"UTF-8"</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">title</span>&gt;</span>案例:监听域对象的属性变更<span class="tag">&lt;/<span class="name">title</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;/<span class="name">head</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">h3</span> <span class="attr">align</span>=<span class="string">"center"</span>&gt;</span>测试域对象属性信息监听器的页面<span class="tag">&lt;/<span class="name">h3</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">%</span></span></span><br><span class="line"><span class="tag">			<span class="attr">getServletContext</span>()<span class="attr">.setAttribute</span>("<span class="attr">name</span>", "<span class="attr">YUbuntu0109</span>");</span></span><br><span class="line"><span class="tag">			<span class="attr">getServletContext</span>()<span class="attr">.setAttribute</span>("<span class="attr">name</span>", "<span class="attr">https:</span>//<span class="attr">YUbuntu0109.github.io</span>");</span></span><br><span class="line"><span class="tag">			<span class="attr">getServletContext</span>()<span class="attr">.removeAttribute</span>("<span class="attr">name</span>");</span></span><br><span class="line"><span class="tag">			</span></span><br><span class="line"><span class="tag">			<span class="attr">session.setAttribute</span>("<span class="attr">name</span>", "<span class="attr">YUbuntu0109</span>");</span></span><br><span class="line"><span class="tag">			<span class="attr">session.setAttribute</span>("<span class="attr">name</span>","<span class="attr">https:</span>//<span class="attr">YUbuntu0109.github.io</span>");</span></span><br><span class="line"><span class="tag">			<span class="attr">session.removeAttribute</span>("<span class="attr">name</span>");</span></span><br><span class="line"><span class="tag">			</span></span><br><span class="line"><span class="tag">			<span class="attr">request.setAttribute</span>("<span class="attr">name</span>", "<span class="attr">YUbuntu0109</span>");</span></span><br><span class="line"><span class="tag">			<span class="attr">request.setAttribute</span>("<span class="attr">name</span>", "<span class="attr">https:</span>//<span class="attr">YUbuntu0109.github.io</span>");</span></span><br><span class="line"><span class="tag">			<span class="attr">request.removeAttribute</span>("<span class="attr">name</span>");		</span></span><br><span class="line"><span class="tag">		%&gt;</span></span><br><span class="line">	<span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br></pre></td></tr></table></figure>
</li>
</ol>
<ol>
<li><p><em>MyAttributeListener.java : 用于监听各个域对象属性的变更.</em></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@ClassName</span>: MyAttributeListener</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@Description</span>: 监听域对象的属性变更</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@author</span>: HuangYuhui</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@date</span>: May 3, 2019 4:18:40 PM</span></span><br><span class="line"><span class="comment"> * </span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"></span><br><span class="line"><span class="meta">@WebListener</span>(<span class="string">"/MyAttributeListener"</span>)</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">MyAttributeListener</span></span></span><br><span class="line"><span class="class">		<span class="keyword">implements</span> <span class="title">ServletContextAttributeListener</span>, <span class="title">HttpSessionAttributeListener</span>, <span class="title">ServletRequestAttributeListener</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">attributeAdded</span><span class="params">(ServletContextAttributeEvent event)</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"ServletContext 添加属性: name="</span> + event.getServletContext().getAttribute(event.getName()));</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">attributeReplaced</span><span class="params">(ServletContextAttributeEvent event)</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"ServletContext 替换属性: name="</span> + event.getServletContext().getAttribute(event.getName()));</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">attributeRemoved</span><span class="params">(ServletContextAttributeEvent event)</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"ServletContext 移除属性: "</span> + event.getName());</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">attributeAdded</span><span class="params">(ServletRequestAttributeEvent srae)</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"HttpRequest 添加属性: name="</span> + srae.getServletRequest().getAttribute(srae.getName()));</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">attributeReplaced</span><span class="params">(ServletRequestAttributeEvent srae)</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"HttpRequest 替换属性: name="</span> + srae.getServletRequest().getAttribute(srae.getName()));</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">attributeRemoved</span><span class="params">(ServletRequestAttributeEvent srae)</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"HttpRequest 移除属性: "</span> + srae.getName());</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">attributeAdded</span><span class="params">(HttpSessionBindingEvent event)</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"HttpSession 添加属性: name="</span> + event.getSession().getAttribute(event.getName()));</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">attributeReplaced</span><span class="params">(HttpSessionBindingEvent event)</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"HttpSession 替换属性: name="</span> + event.getSession().getAttribute(event.getName()));</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">attributeRemoved</span><span class="params">(HttpSessionBindingEvent event)</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"HttpSession 移除属性: "</span> + event.getName());</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
</li>
<li><p><em>程序运行结果如下所示.</em></p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">ServletContext 添加属性: name=YUbuntu0109</span><br><span class="line">ServletContext 替换属性: name=https://YUbuntu0109.github.io</span><br><span class="line">ServletContext 移除属性: name</span><br><span class="line">HttpSession 添加属性: name=YUbuntu0109</span><br><span class="line">HttpSession 替换属性: name=https://YUbuntu0109.github.io</span><br><span class="line">HttpSession 移除属性: name</span><br><span class="line">HttpRequest 添加属性: name=YUbuntu0109</span><br><span class="line">HttpRequest 替换属性: name=https://YUbuntu0109.github.io</span><br><span class="line">HttpRequest 移除属性: name</span><br></pre></td></tr></table></figure>
</li>
</ol>
<h4 id="案例-统计当前在线人数名单"><a href="#案例-统计当前在线人数名单" class="headerlink" title="案例-统计当前在线人数名单"></a>案例-统计当前在线人数名单</h4><p><em>案例描述 : 在上述<code>统计当前在线人数</code>的案例中,实际上统计的是Web应用当前的所有会话的数目.它无法统计所有所有在线用户的具体名单! 下面我们通过使用<code>HttpSessionBindingListener</code>接口不仅可以统计在线用户的数量,还可以统计在线用户的名单.</em></p>
<ol>
<li><p><em>login.jsp : 用户登录页面.</em></p>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">%@</span> <span class="attr">page</span> <span class="attr">language</span>=<span class="string">"java"</span> <span class="attr">contentType</span>=<span class="string">"text/html; charset=UTF-8"</span></span></span><br><span class="line"><span class="tag">    <span class="attr">pageEncoding</span>=<span class="string">"UTF-8"</span>%&gt;</span></span><br><span class="line"><span class="meta">&lt;!DOCTYPE <span class="meta-keyword">html</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;<span class="name">head</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">meta</span> <span class="attr">charset</span>=<span class="string">"UTF-8"</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">title</span>&gt;</span>案例:统计登录用户的在线名单<span class="tag">&lt;/<span class="name">title</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;/<span class="name">head</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">h3</span> <span class="attr">align</span>=<span class="string">"center"</span>&gt;</span>用户登录页面<span class="tag">&lt;/<span class="name">h3</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">hr</span>/&gt;</span></span><br><span class="line">			<span class="tag">&lt;<span class="name">form</span> <span class="attr">action</span>=<span class="string">"LoginServlet"</span> <span class="attr">method</span>=<span class="string">"post"</span>&gt;</span></span><br><span class="line">				<span class="tag">&lt;<span class="name">table</span> <span class="attr">width</span>=<span class="string">"280px"</span> <span class="attr">cellpadding</span>=<span class="string">"0"</span> <span class="attr">align</span>=<span class="string">"center"</span>&gt;</span></span><br><span class="line">					 <span class="tag">&lt;<span class="name">tr</span>&gt;</span></span><br><span class="line">					 	<span class="tag">&lt;<span class="name">td</span> <span class="attr">height</span>=<span class="string">"30"</span> <span class="attr">align</span>=<span class="string">"center"</span>&gt;</span>用户名<span class="tag">&lt;/<span class="name">td</span>&gt;</span></span><br><span class="line">					 	<span class="tag">&lt;<span class="name">td</span>&gt;</span><span class="tag">&lt;<span class="name">input</span> <span class="attr">type</span>=<span class="string">"text"</span> <span class="attr">name</span>=<span class="string">"userName"</span>/&gt;</span><span class="tag">&lt;/<span class="name">td</span>&gt;</span></span><br><span class="line">					 <span class="tag">&lt;/<span class="name">tr</span>&gt;</span></span><br><span class="line">					 <span class="tag">&lt;<span class="name">tr</span>&gt;</span></span><br><span class="line">					 	<span class="tag">&lt;<span class="name">td</span> <span class="attr">height</span>=<span class="string">"30"</span> <span class="attr">align</span>=<span class="string">"center"</span>&gt;</span>密<span class="symbol">&amp;nbsp;</span>码<span class="tag">&lt;/<span class="name">td</span>&gt;</span></span><br><span class="line">					 	<span class="tag">&lt;<span class="name">td</span>&gt;</span><span class="tag">&lt;<span class="name">input</span> <span class="attr">type</span>=<span class="string">"password"</span> <span class="attr">name</span>=<span class="string">"userPassword"</span>/&gt;</span><span class="tag">&lt;/<span class="name">td</span>&gt;</span></span><br><span class="line">					 <span class="tag">&lt;/<span class="name">tr</span>&gt;</span></span><br><span class="line">					 <span class="tag">&lt;<span class="name">tr</span>&gt;</span></span><br><span class="line">					 	<span class="tag">&lt;<span class="name">td</span> <span class="attr">height</span>=<span class="string">"50"</span> <span class="attr">colspan</span>=<span class="string">"2"</span> <span class="attr">align</span>=<span class="string">"center"</span>&gt;</span></span><br><span class="line">					 		<span class="tag">&lt;<span class="name">input</span> <span class="attr">type</span>=<span class="string">"submit"</span> <span class="attr">value</span>=<span class="string">"登录"</span>/&gt;</span><span class="symbol">&amp;nbsp;</span><span class="symbol">&amp;nbsp;</span><span class="symbol">&amp;nbsp;</span><span class="symbol">&amp;nbsp;</span></span><br><span class="line">					 		<span class="tag">&lt;<span class="name">input</span> <span class="attr">type</span>=<span class="string">"reset"</span> <span class="attr">value</span>=<span class="string">"重置"</span>/&gt;</span></span><br><span class="line">					 		<span class="tag">&lt;<span class="name">span</span> <span class="attr">style</span>=<span class="string">"font-size:13px;color:red"</span>&gt;</span>$&#123;errorMsg &#125;<span class="tag">&lt;/<span class="name">span</span>&gt;</span></span><br><span class="line">					 	<span class="tag">&lt;/<span class="name">td</span>&gt;</span></span><br><span class="line">					 <span class="tag">&lt;/<span class="name">tr</span>&gt;</span></span><br><span class="line">				<span class="tag">&lt;/<span class="name">table</span>&gt;</span></span><br><span class="line">			<span class="tag">&lt;/<span class="name">form</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br></pre></td></tr></table></figure>
</li>
<li><p><em>User.java : 封装用户信息.</em></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> pers.huangyuhui.servletlistener.example.onlinenumber2;</span><br><span class="line"></span><br><span class="line"><span class="keyword">import</span> javax.servlet.http.HttpSessionBindingEvent;</span><br><span class="line"><span class="keyword">import</span> javax.servlet.http.HttpSessionBindingListener;</span><br><span class="line"></span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@ClassName</span>: User</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@Description</span>: 封装用户信息</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@author</span>: HuangYuhui</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@date</span>: May 4, 2019 9:10:47 AM</span></span><br><span class="line"><span class="comment"> * </span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">User</span> <span class="keyword">implements</span> <span class="title">HttpSessionBindingListener</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">	<span class="keyword">private</span> String id;</span><br><span class="line">	<span class="keyword">private</span> String username;</span><br><span class="line">	<span class="keyword">private</span> String password;</span><br><span class="line"></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="title">User</span><span class="params">(String id, String name, String password)</span> </span>&#123;</span><br><span class="line">		<span class="keyword">this</span>.id = id;</span><br><span class="line">		<span class="keyword">this</span>.username = name;</span><br><span class="line">		<span class="keyword">this</span>.password = password;</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="function"><span class="keyword">public</span> String <span class="title">getId</span><span class="params">()</span> </span>&#123;</span><br><span class="line">		<span class="keyword">return</span> id;</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setId</span><span class="params">(String id)</span> </span>&#123;</span><br><span class="line">		<span class="keyword">this</span>.id = id;</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="function"><span class="keyword">public</span> String <span class="title">getUsername</span><span class="params">()</span> </span>&#123;</span><br><span class="line">		<span class="keyword">return</span> username;</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setUsername</span><span class="params">(String username)</span> </span>&#123;</span><br><span class="line">		<span class="keyword">this</span>.username = username;</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="function"><span class="keyword">public</span> String <span class="title">getPassword</span><span class="params">()</span> </span>&#123;</span><br><span class="line">		<span class="keyword">return</span> password;</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setPassword</span><span class="params">(String password)</span> </span>&#123;</span><br><span class="line">		<span class="keyword">this</span>.password = password;</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">valueBound</span><span class="params">(HttpSessionBindingEvent event)</span> </span>&#123;</span><br><span class="line">		<span class="comment">// System.out.println("将新用户添加到在线名单 : " + event.getName() + "=" + event.getValue());</span></span><br><span class="line">		OnlineUser.getInstance().addUser(<span class="keyword">this</span>);</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="meta">@Override</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">valueUnbound</span><span class="params">(HttpSessionBindingEvent event)</span> </span>&#123;</span><br><span class="line">		<span class="comment">// System.out.println("从在线名单中移除该用户 : " + event.getName() + "=" + event.getValue());</span></span><br><span class="line">		OnlineUser.getInstance().removeUser(<span class="keyword">this</span>);</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
</li>
<li><p><em>OnlineUser.java : 用于存储和获取在线用户列表.</em></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> pers.huangyuhui.servletlistener.example.onlinenumber2;</span><br><span class="line"></span><br><span class="line"><span class="keyword">import</span> java.util.HashMap;</span><br><span class="line"><span class="keyword">import</span> java.util.Map;</span><br><span class="line"></span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@ClassName</span>: OnlineUser</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@Description</span>: 存储及获取在线用户列表</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@author</span>: HuangYuhui</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@date</span>: May 4, 2019 9:14:09 AM</span></span><br><span class="line"><span class="comment"> * </span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">OnlineUser</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">	<span class="function"><span class="keyword">private</span> <span class="title">OnlineUser</span><span class="params">()</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="keyword">private</span> <span class="keyword">static</span> OnlineUser instance = <span class="keyword">new</span> OnlineUser();</span><br><span class="line"></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> OnlineUser <span class="title">getInstance</span><span class="params">()</span> </span>&#123;</span><br><span class="line">		<span class="keyword">return</span> instance;</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="keyword">private</span> Map&lt;String, String&gt; userMap = <span class="keyword">new</span> HashMap&lt;&gt;();</span><br><span class="line"></span><br><span class="line">	<span class="comment">// 将用户添加至在线列表</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">addUser</span><span class="params">(User user)</span> </span>&#123;</span><br><span class="line">		userMap.put(user.getId(), user.getUsername());</span><br><span class="line"></span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="comment">// 将用户从在线列表中移除</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">removeUser</span><span class="params">(User user)</span> </span>&#123;</span><br><span class="line">		userMap.remove(user.getId());</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="comment">// 返回在线的用户列表</span></span><br><span class="line">	<span class="function"><span class="keyword">public</span> Map&lt;String, String&gt; <span class="title">getOnlineUsers</span><span class="params">()</span> </span>&#123;</span><br><span class="line">		<span class="keyword">return</span> userMap;</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
</li>
<li><p><em>LoginServlet.java : 处理用户登录请求.</em></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> pers.huangyuhui.servletlistener.example.onlinenumber2;</span><br><span class="line"></span><br><span class="line"><span class="keyword">import</span> java.io.IOException;</span><br><span class="line"><span class="keyword">import</span> java.util.Map;</span><br><span class="line"><span class="keyword">import</span> java.util.UUID;</span><br><span class="line"></span><br><span class="line"><span class="keyword">import</span> javax.servlet.ServletException;</span><br><span class="line"><span class="keyword">import</span> javax.servlet.annotation.WebServlet;</span><br><span class="line"><span class="keyword">import</span> javax.servlet.http.HttpServlet;</span><br><span class="line"><span class="keyword">import</span> javax.servlet.http.HttpServletRequest;</span><br><span class="line"><span class="keyword">import</span> javax.servlet.http.HttpServletResponse;</span><br><span class="line"></span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@ClassName</span>: LoginServlet</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@Description</span>: 处理用户登录请求</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@author</span>: HuangYuhui</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@date</span>: May 4, 2019 9:30:23 AM</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="meta">@WebServlet</span>(<span class="string">"/LoginServlet"</span>)</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">LoginServlet</span> <span class="keyword">extends</span> <span class="title">HttpServlet</span> </span>&#123;</span><br><span class="line">	<span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">long</span> serialVersionUID = <span class="number">1L</span>;</span><br><span class="line"></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="title">LoginServlet</span><span class="params">()</span> </span>&#123;</span><br><span class="line">		<span class="keyword">super</span>();</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">doGet</span><span class="params">(HttpServletRequest request, HttpServletResponse response)</span></span></span><br><span class="line"><span class="function">			<span class="keyword">throws</span> ServletException, IOException </span>&#123;</span><br><span class="line"></span><br><span class="line">		request.setCharacterEncoding(<span class="string">"utf-8"</span>);</span><br><span class="line">		String username = request.getParameter(<span class="string">"userName"</span>);</span><br><span class="line">		String password = request.getParameter(<span class="string">"userPassword"</span>);</span><br><span class="line"></span><br><span class="line">		<span class="keyword">if</span> (username != <span class="keyword">null</span> &amp;&amp; !username.trim().equals(<span class="string">""</span>)) &#123;</span><br><span class="line">			User user = <span class="keyword">new</span> User(UUID.randomUUID().toString(), username, password);</span><br><span class="line">			request.getSession().setAttribute(<span class="string">"user"</span>, user);</span><br><span class="line"></span><br><span class="line">			Map&lt;String, String&gt; onlineUsers = OnlineUser.getInstance().getOnlineUsers();</span><br><span class="line">			request.setAttribute(<span class="string">"onlineUsers"</span>, onlineUsers);</span><br><span class="line"></span><br><span class="line">			request.getRequestDispatcher(<span class="string">"/showOnlineUsers.jsp"</span>).forward(request, response);</span><br><span class="line"></span><br><span class="line">		&#125; <span class="keyword">else</span> &#123;</span><br><span class="line"></span><br><span class="line">			request.setAttribute(<span class="string">"errorMsg"</span>, <span class="string">"用户名不能为空 !"</span>);</span><br><span class="line">			request.getRequestDispatcher(<span class="string">"/login.jsp"</span>).forward(request, response);</span><br><span class="line">		&#125;</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">doPost</span><span class="params">(HttpServletRequest request, HttpServletResponse response)</span></span></span><br><span class="line"><span class="function">			<span class="keyword">throws</span> ServletException, IOException </span>&#123;</span><br><span class="line">		doGet(request, response);</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
</li>
<li><p><em>LogoutServlet.java : 注销用户登录信息.</em></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">package</span> pers.huangyuhui.servletlistener.example.onlinenumber2;</span><br><span class="line"></span><br><span class="line"><span class="keyword">import</span> java.io.IOException;</span><br><span class="line"><span class="keyword">import</span> java.util.Map;</span><br><span class="line"></span><br><span class="line"><span class="keyword">import</span> javax.servlet.ServletException;</span><br><span class="line"><span class="keyword">import</span> javax.servlet.annotation.WebServlet;</span><br><span class="line"><span class="keyword">import</span> javax.servlet.http.HttpServlet;</span><br><span class="line"><span class="keyword">import</span> javax.servlet.http.HttpServletRequest;</span><br><span class="line"><span class="keyword">import</span> javax.servlet.http.HttpServletResponse;</span><br><span class="line"></span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@ClassName</span>: LogoutServlet</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@Description</span>: 注销用户登录信息</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@author</span>: HuangYuhui</span></span><br><span class="line"><span class="comment"> * <span class="doctag">@date</span>: May 4, 2019 9:54:27 AM</span></span><br><span class="line"><span class="comment"> *</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="meta">@WebServlet</span>(<span class="string">"/LogoutServlet"</span>)</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">LogoutServlet</span> <span class="keyword">extends</span> <span class="title">HttpServlet</span> </span>&#123;</span><br><span class="line">	<span class="keyword">private</span> <span class="keyword">static</span> <span class="keyword">final</span> <span class="keyword">long</span> serialVersionUID = <span class="number">1L</span>;</span><br><span class="line"></span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="title">LogoutServlet</span><span class="params">()</span> </span>&#123;</span><br><span class="line">		<span class="keyword">super</span>();</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">doGet</span><span class="params">(HttpServletRequest request, HttpServletResponse response)</span></span></span><br><span class="line"><span class="function">			<span class="keyword">throws</span> ServletException, IOException </span>&#123;</span><br><span class="line"></span><br><span class="line">		request.getSession().removeAttribute(<span class="string">"user"</span>);</span><br><span class="line"></span><br><span class="line">		Map&lt;String, String&gt; onlineUsers = OnlineUser.getInstance().getOnlineUsers();</span><br><span class="line">		request.setAttribute(<span class="string">"onlineUsers"</span>, onlineUsers);</span><br><span class="line">		request.getRequestDispatcher(<span class="string">"/showOnlineUsers.jsp"</span>).forward(request, response);</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">	<span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">doPost</span><span class="params">(HttpServletRequest request, HttpServletResponse response)</span></span></span><br><span class="line"><span class="function">			<span class="keyword">throws</span> ServletException, IOException </span>&#123;</span><br><span class="line">		doGet(request, response);</span><br><span class="line">	&#125;</span><br><span class="line"></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
</li>
<li><p><em>showOnlineUsers.jsp : 显示所有用户的登录信息以及当前登录的用户.</em></p>
<figure class="highlight html"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag">&lt;<span class="name">%@</span> <span class="attr">page</span> <span class="attr">language</span>=<span class="string">"java"</span> <span class="attr">contentType</span>=<span class="string">"text/html; charset=UTF-8"</span></span></span><br><span class="line"><span class="tag">    <span class="attr">pageEncoding</span>=<span class="string">"UTF-8"</span>%&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">%@taglib</span> <span class="attr">prefix</span>=<span class="string">"c"</span> <span class="attr">uri</span>=<span class="string">"http://java.sun.com/jsp/jstl/core"</span> %&gt;</span></span><br><span class="line"><span class="meta">&lt;!DOCTYPE <span class="meta-keyword">html</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;<span class="name">html</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;<span class="name">head</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">meta</span> <span class="attr">charset</span>=<span class="string">"UTF-8"</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">title</span>&gt;</span>应用案例:统计登录用户的在线名单<span class="tag">&lt;/<span class="name">title</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;/<span class="name">head</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;<span class="name">body</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">h3</span> <span class="attr">align</span>=<span class="string">"center"</span>&gt;</span>用户在线名单如下所示<span class="tag">&lt;/<span class="name">h3</span>&gt;</span></span><br><span class="line">			<span class="tag">&lt;<span class="name">c:choose</span>&gt;</span></span><br><span class="line">				<span class="tag">&lt;<span class="name">c:when</span> <span class="attr">test</span>=<span class="string">"$&#123;sessionScope.user == null &#125;"</span>&gt;</span></span><br><span class="line">					<span class="tag">&lt;<span class="name">a</span> <span class="attr">href</span>=<span class="string">"$&#123;pageContext.request.contextPath &#125;/login.jsp"</span>&gt;</span>登录<span class="tag">&lt;/<span class="name">a</span>&gt;</span><span class="tag">&lt;<span class="name">br</span>&gt;</span></span><br><span class="line">				<span class="tag">&lt;/<span class="name">c:when</span>&gt;</span></span><br><span class="line">				<span class="tag">&lt;<span class="name">c:otherwise</span>&gt;</span></span><br><span class="line">					你已成功登录! 欢迎你: $&#123;sessionScope.user.username &#125;</span><br><span class="line">				 	<span class="tag">&lt;<span class="name">a</span> <span class="attr">href</span>=<span class="string">"$&#123;pageContext.request.contextPath &#125;/LogoutServlet"</span>&gt;</span>退出<span class="tag">&lt;/<span class="name">a</span>&gt;</span></span><br><span class="line">				<span class="tag">&lt;/<span class="name">c:otherwise</span>&gt;</span></span><br><span class="line">			<span class="tag">&lt;/<span class="name">c:choose</span>&gt;</span></span><br><span class="line">		<span class="tag">&lt;<span class="name">hr</span>/&gt;</span></span><br><span class="line">			<span class="tag">&lt;<span class="name">c:forEach</span> <span class="attr">var</span>=<span class="string">"user"</span> <span class="attr">items</span>=<span class="string">"$&#123;requestScope.onlineUsers &#125;"</span>&gt;</span></span><br><span class="line">				<span class="tag">&lt;<span class="name">p</span> <span class="attr">align</span>=<span class="string">'center'</span>&gt;</span>用户名: $&#123;user.value&#125;<span class="tag">&lt;/<span class="name">p</span>&gt;</span></span><br><span class="line">			<span class="tag">&lt;/<span class="name">c:forEach</span>&gt;</span></span><br><span class="line">	<span class="tag">&lt;/<span class="name">body</span>&gt;</span></span><br><span class="line"><span class="tag">&lt;/<span class="name">html</span>&gt;</span></span><br></pre></td></tr></table></figure>
</li>
<li><p><em>程序运行效果示例图.</em></p>
<figure class="image-bubble">
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                    <div class="overlay"></div>
                    <img src="/2019/05/02/Java-web-Servlet-listener/Servlet事件监听器案例-统计当前在线人数名单.PNG" alt title>
                </div>
                <div class="image-caption"></div>
            </figure>
</li>
</ol>
<h3 id="感知被HttpSession绑定的事件监听器"><a href="#感知被HttpSession绑定的事件监听器" class="headerlink" title="感知被HttpSession绑定的事件监听器"></a>感知被HttpSession绑定的事件监听器</h3><p><em>暂略写 ..</em></p>

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    <p>扫一扫，分享到微信</p>
    <img src="//api.qrserver.com/v1/create-qr-code/?data=https://yubuntu0109.github.io/2019/05/02/Java-web-Servlet-listener/" alt="微信分享二维码">
</div>




    <script src="//cdn.bootcss.com/node-waves/0.7.4/waves.min.js"></script>
<script>
var BLOG = { ROOT: '/', SHARE: true, REWARD: true };


</script>

<script src="//unpkg.com/hexo-theme-material-indigo@latest/js/main.min.js"></script>


<div class="search-panel" id="search-panel">
    <ul class="search-result" id="search-result"></ul>
</div>
<template id="search-tpl">
<li class="item">
    <a href="{path}" class="waves-block waves-effect">
        <div class="title ellipsis" title="{title}">{title}</div>
        <div class="flex-row flex-middle">
            <div class="tags ellipsis">
                {tags}
            </div>
            <time class="flex-col time">{date}</time>
        </div>
    </a>
</li>
</template>

<script src="//unpkg.com/hexo-theme-material-indigo@latest/js/search.min.js" async></script>








<script>
(function() {
    var OriginTitile = document.title, titleTime;
    document.addEventListener('visibilitychange', function() {
        if (document.hidden) {
            document.title = 'Where are you going ?';
            clearTimeout(titleTime);
        } else {
            document.title = 'As long as you love me ~';
            titleTime = setTimeout(function() {
                document.title = OriginTitile;
            },2000);
        }
    });
})();
</script>



</body>
</html>
